Multiplex radio system



Aug. 20, 1929. R HElSlNG 1,724,922

MULT IPLEX RADIO SYSTEM Filed D80. 31, 1923 670000 fif/f 1P2 E5-J700000- Rag/720044 00/0/27;

Patented Aug. 20, 1929.

RAYMOND A. HEISING, OF MILLBO RNL NEW JERSEY, ASSIGNOR TO WESTERN ELEC-TRIO COMPANY, INCORPORATED,- F 1\TEW YORK, N. Y., A CORPORATION OF NEWYORK.

MULTIPLEX RADIO SYSTEM."

Application filed December 31, Q23. Serial No. 683,629.

This invention relates to amultiplex radio system and moreparticularlytoa method of and means for operating a terminalsta tiontherefor which permits simultaneous 5 two-way communications overthe-several channels without interference.

The present invention provides a terminal station for multiplexoperation in whichthe frequencies of the carrier waves used for 1Qtwo-way communication over the different channels are so chosen that-byutilizing at" the receiving sets frequency discrimination alone incertain channels and the direct ve properties of loop antennae incombination with frequency selectivity in the other channels, all of thechannels may be simultane-' ously operated without interference undercertain conditions, or anumber of. two way communications may besimultaneously maintained under. all conditions.

In accordance with this invention each receiving set comprises a loopantenna sharply tuned to the frequency to be received, associated with asuccess ve detee tion system using a predeterm ned inter mediatefrequency.

- selective circuits being relied uponl'to pres vent interference due tothe outgoi-ng and; incoming signal waves of the other channels.

The loop antennae of the-lot'her receiving sets are used so that theyare each non; receptive for the transmitted signal wave which mostnearly approaches the frequency of the signal wave to be received by.it, 'while the high and intermediate frequency -sele c-.

tive circuits of the set are relied upon to prevent interference due tothe other Out-. going andincoming waves. In this manner the directiveproperties or loop antennae and frequency discrimination. are jointlyused to prevent interference.

For operation between the terminal statioii described above, and apluralityof'remote fixed stations, it would bea fairlv' simple matter tolocate the distant stations relatively to the receivers and transm ttersof the terminal station so that two-Way communications could besimultaneously maintained over all channels at all times.

Ina system including mobile distant stations such as aeroplane or shipstations, it would "be impossible to locate the transmitters andreceivers so that communication could be maintained over all of thechannels; because of the movement of the distant stationsand the factthat only one channel can be operated in all directions. However, bylocating the receiving sets for the other channels so that the receptiveangles or segments of their antennae overlap and using; them to receivesuccessive portionsnf the incoming message it is possible to maintainone or more additional two-way communications.

' One" object of this invention is to provide a terminal station formultiplex radio systems in which frequency discrimination alone and thedirective properties of loop antennae combined with frequencyselectivity may be. used 'to prevent interference between channels.

Another'object is the provision of a radio terminal station whichpermits a number of two-way communicating channels to be simultaneouslyoperated in any direction without interference.

Still'another obj ect is to provide receiving sets for a terminalstation in which frequencyselection and the directive properties of loopantenna "are jointly used to discriminate between several communicatingchannels.

Afeature of this invention is the provision of an adjustable highfrequency transformer.

Fora complete disclosure of the invention and-the operation of thevarious parts, refere'nce'should be made to the following descriptionread in conjunction with the at tached drawing;

1 Fig 1 shows diagrammatically a terminal station embodying theinvention;

Fig. 2 shows the complete circuit arrangement for onechannel includingalternatives of certain features thereof; and

Fig. 3 illustrates an adjustable high frequency transformer which isused in the receiving circuits.

Throughout this specification A and R will be used to identifyrespectively, a transmitting antenna, and a main receiving set,

a loop antenna 1, including an adjustable tuning condenser 2, a radiorecelvlng apparatus 3, provided with a signal. indicating device 4,shown by way of example as a telephone receiver, and an auxiliary radioreceiver B B or 13,. I

Theterminal equipment for the first channel comprises the antennaA andthe cooperative main and auxiliary receivers R and 13,, that for thesecond channel, the antenna A and the cooperative main and auxiliaryreceivers R and B and that for the third channel, the antenna A and themain and auxiliary receivers R and B The frequencies of the incoming andoutgoing carrier waves for all the channels are different, and thefrequencies of the carrier waves respectively radiated from the antenneeA A and A differ from the frequencies of the incoming carrier waves forthe corresponding channels by readily selectable frequencies aboveaudibility.

The antenna of each receiver is sharply tuned to the incoming frequencywhich it is adapted to receive and the antenna of each auxiliaryreceiver is sharply tuned to the frequency of the corresponding outgoingcarrier wave of the channe p The auxiliary receiver'for each channelisassoclated with the mam receiver by a coup- I ling coil or transformer6. The purpose of this arrangement will be described herein after.

apparatus for one channel comprising a transmitter consisting of anantenna A connected to ground 7 by a lead includin a coupling coil 8, acondenser 9 and an in noknown apparatus for supplying current to theantenna A whereby radio telegraph or radio telephone signals may betransmitted. For example, the system shown in Patent No. 1,442,147, Jan.16, 1923 to R. A. Heising may be used for radio telephone transmissionwhile a systems'imilar to that described in Patent 1,349,729, August 17,

Fig. 2 illustrates the arrangement of the 1920 to E. L. Nelson may beused for radio telegraph transmission.

Condenser 9 and inductance 10 are included in the antenna circuit torender it highly selective or stiff for the signal frequency radiated,whereby intermodulation between the different channels is prevented anda minimum of crosstalk results.

The auxiliary receiver B comprises an antenna 5 coupled by a tunedcircuit 13 to the input of an amplifier 1 1. The coupling circuit 13 issharply tuned to the frequency of the carrier wave radiated from theantenna A The output circuit of the amplifier 14: includes a circuit 15also sharply tuned to the carrier frequency radiated from the antenna AThe main radio receiver is adapted to operate on the basis of the wellknown successive detection system, in which the incoming signal wave iscombined with other oscillations to produce an auxiliary. intermewave byan adjustable c'ondenser2. The re- 5 ceived high frequency waves areamplified by the amplifiers 16 and 17 and impressed upon the inputcircuit of the detector 18.

However, since the principles of this invention are independent of radiofrequency amplification, the question as to whether radio frequencyamplifiers are'to be used and the number of stages to be employed in anycase' is a matter to bedetermined for each installation. The devices 16,17 and 18 are inter coupled by transformers especially adapted for usewith high frequency currents. The

7 design of this transformer will be described below with reference toFig. 3.

The'input circuit of the detector 18 includes one coil of the coupler ortransformer 6 the other coil of which is included in the tuned circuit15.

The output circuit of the device 18 includes a coupling inductance l9shunted by an anti-resonant circuit 20 which is of high impedance forthe auxiliary intermediate frequency, but provides a low impedance pathfor other frequencies.

' The resultant intermediate I frequency wave is amplified by theamplifiers 21 and 22, transmitted through the selective means 23, anddetected by the device 24.

The selective means 23 may be either a tuned circuit, resonant to theintermediate frequency, or a filter adapted to freely pass a frequencyband including the intermediate frequency wave while suppressingfrequencies outside this band.

The low frequency currents resulting from the second stage of detectionare supplied to the indicating device 4: which may be of any well knowndesign, but is herein shown as a telephone receiver.

In a radio receiving circuit employing high frequency amplification asdescribed above, it is desirable to intercouple the amplifying devicesby means of circuits tuned to the incoming signal waves. Thus, thecoupling circuits between the amplifiers 16 and 17 and between theamplifier 17 and de tector 18 should be selective of the frequency ofthe signal waves received by the an tenna 1. Since the input and outputcircuits of the amplifiers are both tuned to the same frequency,considerable difliculty has been encountered due to the production ofundesired oscillations or singing in the amplifier circuits. Thissinging is largely due to a coupling effect between the input and outputcircuits of the amplifier.

The usual method for preventing singing in amplifier circuits is toinclude a resistance at some point in the coupled circuits or else toconstruct the primary winding of the transformers of resistance wire. Asshown in this figure a transformer provided with adjustable means forcontrolling the electrical characteristics of its primary and secondarycircuits is used to intercouple the amplifiers 16 and 17 and to couplethe latter to the detector 18.

The coupling transformer, shown in detail in Fig. 3, comprises an aircore transformer having a primary and a secondary winding, 30 and 31,respectively, wound on an insulating core 32, secured to a supportingframe 3%. The supporting frame as shown, is of insulating material andmay be of any such material and of any form. Arms 35 of the frame 34 areadapted to support elements 36 and 37 axially of the core 32.

The windings 30 and 31 when used with discharge devices 16, 17 and 18are each wound to cooperate with the internal capacity of the associateddevice to constitute a tuned circuit. When used with other forms of highimpedance amplifiers and detectors, such winding should be designed tohave the necessary inductance and distributed capacity to determine itstuning.

The element 36 consists of a spirally wound laminated iron strip orribbon with its convolutions spaced apart. This ele ment is carried by athreaded shank engaging a screw-threaded opening in one of the arms 35and is associated with the primary winding 30.

A conductive element 37, which may be a copper or brass rod, is providedwith a screw thread to engage a screw-threaded opening in the other arm35. The area of the rod 37 should be as large as possible, and

preferably its diameter should be only slightly less than the internaldiameter of the secondary winding 31.

The transformer should be mounted so that the only coupling between thewindings 30 and 31 is that due to their mutual inductance. In otherwords the supporting means for the windings should intro ducesubstantially no coupling effect between the primary and secondarycircuits of the transformer.

High frequency current flowing-through the primary winding 30 willproduce a mag netic field in the space surrounding it. Vith the element36 lying in this magnetic field, losses will be introduced into theprimary circuit due to eddy currents traversing the ribbon winding andto the hysteresis of the iron. These losses appear as an effectiveresistance load in the primary circuit.

Because of the high frequencies involved, the iron does not function todecrease the reluctance of the magnetic circuit and hence the reactanceof the primary circuit and the mutual inductance between the transformerwindings remains substantially constant.

By varying the position of the element 36 relatively to the Winding 30the value of the losses in the ribbon winding and hence the amount ofthe resistance load introduced into the primary circuit may beregulated.

In a similar manner, high frequency current flowing through thesecondary winding 31 will generate a magnetic field. The rod 37 being ofconductive material functions as a short-circuited winding in which eddycurrents will be produced when this element lies within the magneticfield of winding 31.

Because of the transformer action between the winding 31 and element 37,the magnetic field due to the flow of eddy currents in the element 37will be opposed to the magnetic field resulting from current flow in thewinding 31 and consequently the effective inductance of the winding 31will be decreased.

By adjusting the element 37 relatively to the winding 31, the couplingbetween 31 and 37 can be varied to control the amplitude of the eddycurrents, and hence the value of the inductance thereby introduced intothe secondary circuit. In this manner the tuning of the circuitincluding the winding 31 may be accurately adjusted.

The operation of the system and the function of its various parts willbe clear from the following description of the arrangement shown in Fig.2 which will be c0nsidered as illustrating the apparatus of channel No.1 of a radio telephone system.

It is assumed, for purposes of illustration, that the incoming andoutgoing carrier frequencies used in the different channels are asfollows: channel N o. 1, incoming 708,000 cycles and outgoing 678,000cycles; channel N o. 2, incoming 780,000 cycles and outgoing differs byan angle of approximately 25 degrees; 2nd, the loop antennae aresopositioned and orientated with reference to the transmitting antennaethat the latter always lie within the non-receptive range of both ofthese receiving loop antennae; and 3rd, that the antenna of the secondchannel receiver R is rotatable through a complete circuit, whereby itmay receive in any direction.

The second condition as stated above may be fulfilled by locating theloop antennae of the first and third channel receivers at some distancefrom the'transmitting antenna and at such directions therefrom. that thelines connecting the loop antennae with the transmitting antennae forman angle of 25 which is the same angle as the angular distancebetweentheir respective directions of zero reception. The angle 25 ischosen as an illustrative value only and may in practice vary over alarge range.

The loop antenna of receiver B is. adjusted to receive an incomingcarrier wave of 7 08, 000'cycles modulated in accordance with signals,but at the same time to prevent reception of the outgoing carrier waveof 714,000 cycles.

The outgoing carrier frequency of 678,000 cycles is received by theantenna 5 of the auxiliary receiver B amplified by the device 14 andimpressed by the coupling 0 upon the input circuit of the detector 18.Incoming signal waves received by the loop antenna 1 afterbeingamplified are impressed upon the input circuit of the detector 18.V

The carrier modulated wave of 708,000 cycles is combined with the'unmodulated carrierwave of 678,000 cycles to produce in the outputcircuit of the detector an interimpressed upon the input of the detector24.

The output circuit of'the detector will include'speech currents adaptedto actuate the receiver 4.

Current components of frequencies outside the intermediate frequencyband contained in the output circuit of the detector 18 will be divertedthrough the low impedance path provided by the shunt circuit 20 andhence will not be supplied to the amplifier 21. w

The carrier wave of 750,000 cycles radiated by the antenna A differs by42,000 cycles from that receivable by the antenna 1 and by 72,000 cyclesfrom that receivable by the antenna 5 and hence they will besubstantially suppressed by the selective action of these elements.

'However, should any energy of 750,000 cycles flow through'the antennacircuits 1 and 5, the, resultant current will be considerably attenuatedby the successiveactions of the selective circuits'13 and 15 and whencombined with the transmitted car-. rier Wave for this channel willproduce intermediate frequency waves of 42,000 and 7 2,000 cyclesrespectively which will be suppressed by joint action of the shunt path20 and the filter 23. In a similar manner, any waves of the otherincoming carrier frequencies, i. e., 744,000 cycles and 780,000 cycles,differ from the wave to be received over" the chiannel, underconsideration by. 46,000lcycles andv 72,000 cycles respectively and willbe suppressed by the selective means included in the receiver circuit. I

The second channel, employs incoming andv outgoing frequencies which areboth widely spaced in the frequency spectrum from the carrierfrequencies radiated from the antcnnae A and A and hence the radiofrequency selectivity of the antennae of R and B as well as theselectivity of the different tuned circuits and filter included in' there- 7 ceiving circuit of this channel may be relied upon to. effectivelysuppress the energy received from A and I The nearest incoming frequencyis a weak 744,000 which differs from that received by the antenna 5 of Bby 6000 cycles. The 744,000 cycle wave and its intermediate frequencycurrent of 6000 cycles will be effec tively suppressed by thecooperative action of the high frequency tuning and the intermediateselective currents included in the receiver R The operation of the thirdchannel is identical with that of the first channel. The loop antenna ofthe third channel is always arranged to be non-receptive of the 750,000cycles wave radiated from antenna A The nearest incoming frequency is708,000 cycles which differs from the wave to be received by 36,000cycles. These main and intermediate frequency waves will be suppressedby the selective means included in receivers B andR In the case of asystem including mobilestations two-way communications may be maintainedin all directions over the second channel. Two-way communication may behad overchannel No. 1 until the movable station is in such positionrelatively to receiver B that its antenna is blind or nonreceptive.However, when this occurs the movable station is within the receptiverange of channel No. 3 and, by adjusting the apparatus at the movablestation to cooperate with the third channel apparatus of the terminalstation, two-way communications may be continued over this channel.

Fig. 2 shows two alternative arrangements for supplying oscillation tothe input circuit of the detector 18.

According to one arrangement oscillations of the desired frequencysupplied by a local source 25 are impressed upon the input circuit ofthe detector 18 by the coil 26 in ductively associated with thesecondary winding of the coupling coil 6.

In a second arrangement a wire line 27 may be used to transmit carrieroscillations from the source 11. A tuned circuit 28, resonant to thecarrier waves supplied by the source 11, is inductively associated withthe coil 8 and is included in the line 27 which is provided with a coil29 adapted to be inductively associated with the secondary winding ofthe coupling coil 6 included in the input circuit of the detector 18.

A terminal station for a three-channel system has been described.However, it will be apparent that the priniciples of this invention maybe applied to a system embodying any number of channels.

From the preceding description, it will be seen that the presentinvention provides a terminal station for a multi-channel radio systemadapted to permit simultaneous twoway signaling over all channelswithout in terference, but which is especially effective where it isdesired to maintain a plurality of two-way communications in alldirections between a fixed station and a plurality of' movable stations.

A system embodying certain apparatus and specific details has beendescribed for the purpose of completely and clearly disclosing theprinciples of the invention. However, it is to be understood that thisinvention is not limited to the arrangement or specific featuresdisclosed, but only by the scope of the attached claims.

What is claimed is:

1. In a multiplex radio system, a method of operating a terminalstation, including for each two-way channel a radio transmitter and aradio receiver having a directively selective antenna, which comprisesemploying a wave of different frequency for each transmission, usingwaves for the several channels the frequencies of certain of which aretoo closely spaced to permit frequency selection between them, adjustingcertain antennae to each directively receive an incoming wave whiledirectively preventing the reception of the wave of closely spacedfrequency, and preventing the receptionof all other waves by frequencyselection.

2. A terminal station for a radio system closely spaced to permitfrequency selection between them, each receiver including an antenna fordirectively receiving one 1ncoming wave, for directively preventing thereception of at least one other wave and having associated therewithfrequency selective means for preventing the reception of the remainderof the waves used in the system.

3. A terminal station for a radio system having a plurality of two-waychannels, a transmitter and a receiver for each twoway channel, thefrequencies of certain of the waves used in the system being too closelyspaced to permit frequency selection between them, each receiverincluding a loop antenna and frequency selective means, the frequencyselective means of certain channels being adjusted to permit two-wayconimunications thereover, the loop antennae, respectively, of otherchannels being adjusted to directively receive one wave and to cooperatewith the associated frequency selective means for preventing thereception of the too closely spaced and other waves used in the system.

4. A terminal station for a multi-channel radio system for use with aplurality of mobile stations, comprising a transmitter for each channel,a receiving set for each channel, each receiving set including a loopantenna and frequency selective means, the antenna of one of saidreceiving sets and the selective means associated therewith beingadjustable to receive a desired wave in all directions and to preventreception of all other waves, the antennae of the other receiving setsbeing adjustable to receive desired waves from certain directions, buteach to be at all times non-receptive for certain waves radiated fromsaid transmitters and the selective means associated with each be mgeffective to prevent reception of other undesired waves, the antennae ofsaid other sets being adjustable so that their receptive angular rangesoverlap, whereby a plurality of two-way communications may be maintainedin all directions between said mobile stations and said terminalstation.

5. A terminal station for a multiplex radio system for use with aplurality of mobile stations, comprising a plurality of transmitters, apluralit of receiving sets including a loop antenna and frequency selective means, the antenna of one of said sets and the selective meansassociated therewavein all directions and to preventreception of allother signal waves, and for'the other sets the directive selectivity ofeach loop antennae and the associated frequency .so thattheir receptiveranges overlap whereby one and then the other may be used to maintaincommunications between said mobile stations and said terminal'stationfrom all points of the compass.-

Aterminal station for a' radio system V I having a pluralityof two-Waychannels comwith being adjustable to receive adesiredprisingatransmitter and receiver for each channel, the difierence in frequencyof at least two of the'radio waves employed in said-systemlyingwithinthe range of audi bility, an antenna for one of said receiversdirectionally selective to one of said two waves to the substantialexclusion of the other, and frequency selective means for said receiverwhereby the reception of other waves is prevented. v In witness whereof,I hereunto subscribe my name this 28 day of December A. D., 1923.

' RAYMOND A. HEISING.

